1. Field of the Invention
The present invention relates to a process for removing inks from waste paper. More particularly, the invention relates to a process for deinking waste paper comprising the steps of converting waste paper to a pulp, contacting the pulp with a deinking agent comprising an aqueous dispersion of a surface-active copolymer bearing quaternized nitrogen atoms and removing ink from the pulp.
2. Technology Description
Waste paper has long served as a source of raw fiber material for paper making for the production of a variety of paper and paperboard products. Today, greater utilization of reclaimed fiber has provided incentive for taking steps to upgrade the reclaimed product. These processes include steps to effectively remove ink from waste fibers in order to permit their use in the manufacture of, for example, newsprint and hygiene paper and high quality papers.
Therefore, efficient ink removal is particularly desirable to obtain excellent quality, high value products.
In the course of conventional paper reclamation, the deinking processes essentially comprise the following steps:
1) pulping the waste paper, i.e. fiberizing it in water PA1 2) contacting the pulp with an alkaline aqueous deinking medium containing a chemical deinking agent. PA1 The physical pulping and the alkalinity of the aqueous medium cause at least the partial removal of ink from the pulp fiber. The deinking agent completes this removal and produces an aqueous suspension and/or dispersion of the ink particles. PA1 3) Removing the detached suspended dispersed ink from the pulp. This separation can be carried out by washing and/or flotation techniques well know in the art. PA1 - Conventional inks or oil-based inks are based on organic solvents, mineral oils, hydrocarbons and nitrocellulose. Suitable solvents are for example esters/or ketones, for example ethyl acetate, methyl ethyl ketone and alcohol and organic resins. These conventional inks are most of the time well detached from the fibers during pulping in an alkaline medium and well removed during a subsequent flotation step with an appropriate deinking agent. PA1 - Waterborne inks mainly used in flexographic printing of newspapers have been developing over several years.
Steps (1) and (2) can be performed at least partly at the same time.
There are basically two main different kind of inks:
The reason for the increased use of waterborne printed inks are environmentaly based. There are also safety and economic reasons for using them. Waterborne inks are non-flammable which eliminates the need for expensive safety systems which have to be installed in plants where oil-based inks are used. In addition to that, waterborne inks have the further advantages of reducing pproblems during start-up of the printing machine and increase the possibility of utilization of lower basis weight papers.
However, waterborne inks, more particularly in waterborne flexographic printed newspapers, lead to great deinking difficulties which can make flotation de-inking plants inefficient.
Another difficulty is to pulp a batch of reclaimed paper without any flexographic printed newspaper in it. In fact most of the time the reclaimed waste papers are mixed together and it is impossible or at least uneconomical to separate the two different inks. Or the impact of using some waterborne inks on conventional deinking processes is severe; inclusion of as little as 5% flexographic newspapers into a newsprint recycle furnish, can significantly reduce the brightness of the recycled pulp.
Conventional practice has been to process flexographic newsprint using wash deinking processes. While wash deinking is easy to operate, and requires minimal capital investment, the large volumes of water required make wash deinking an increasingly environmentally unacceptable practice. The paper industry as a whole is under severe pressure to reduce rates of water consumption. As a result the trend in the recycled paper industry is towards use of flotation or hybrid flotation/wash systems for ink removal. Flotation is particularly ill-suited for removal of waterborne ink from recycle newsprint as both the small particle size and hydrophilic nature of the ink result in poor rates of bubble attachment and low separation efficiencies. The poor effectiveness of flotation in removal of waterborne inks is a particular obstacle to recycling newsprint so contaminated, and in some cases restricts the acceptance of the use of waterborne inks as a means to reduce emissions of volatile organic compounds.
There have been proposals describing a two stage process to remove waterborne pigments using a flotation step under acidic conditions followed by a flotation step under alkaline conditions. Maintenance of acid conditions limits the hydrophilicity of the pigment particles, and reduces the degree of dispersion of such inks. The benefit of this procedure is avoidance of the high water consumption of a wash system, however the capital and operating costs of this process are greater than that of a single flotation stage process, and in addition pulping under acidic conditions is difficult if the waste paper contains alkaline fillers such as calcium carbonate.
In Borchardt et al (TAPPI 1994 Pulping Conference, November 6-10, Proceedings pages 1067-1103) many of the difficulties of recycling flexographic newsprint are described in detail; in particular the extremely small size and hydrophilic nature of the pigment particles, and difficulty in removing them by either wash or flotation unit operations. Borchardt also discloses polyacrylates as effective in reducing redepositon of pigment in these applications.
In WO 93/21376 the use of anionic polymers as aides in deinking wastepaper under substantially neutral conditions is described. This reference stresses that its process cannot be used at a pH of greater than 9 as yellowing of the pulped fibers can occur.
U.S. Pat. No. 5,094,716 describes the use of a combination of an anionic surfactant and an anionic dispersant for use in removal of hydrophobic inks in wash processes. This reference does not suggest the use of its process for treatment of hydrophilic inks or the use of a nonionic surfactant.
U.S. Pat. No. 4,599,190 describes the use of polyelectrolyte dispersants in combination with nonionic surfactants in wash deinking of secondary fiber. This process suggested is not a flotation process and it is unclear from the teaching of the reference if it can be used to treat hydrophilic inks.
Canadian patent 2,003,406 relates to a composition for deinking wastepaper comprising an at least partly water soluble polymer.
Despite the above teachings their still exists a need in the art for a process for removing oil-based inks and/or waterborne inks under slightly acidic, neutral or alkaline conditions by using either a flotation technique and/or a washing technique by using a novel deinking agent.